William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

What is occupational asthma?

Asthma is a chronic lung disease characterized by reversible inflammation of the airways (bronchi). In asthma, white blood cells infiltrate the walls of the airways, increased mucus accumulates within the airways, and the muscles surrounding the airways tighten (constrict or "twitch"), resulting in an overall narrowing of the airways. This narrowing of the airways is responsible for the shortness of breath, wheezing, and chest tightness patients with asthma experience during their attacks. Occupational asthma is a type of asthma that is caused by exposure to a particular substance in the workplace. Occupational asthma is not the same as previously diagnosed asthma that is worsened by being at work (this condition would be called work-aggravated asthma).

There are two main types of occupational asthma: one type caused by an agent that stimulates the body's immune system that then triggers asthma (immune-mediated); and another where the agent directly irritates the airways (irritant-induced). Immune-mediated occupational asthma typically has a period of time (latency period) between the workplace exposure and the beginning of symptoms. This latency period can be from a few weeks to several years. In contrast, irritant-induced occupational asthma usually causes symptoms immediately after exposure.

A severe form of irritant-induced occupational asthma is called reactive airways dysfunction syndrome (RADS). This is a condition where the patient suffers a single exposure to a very high concentration of a noxious chemical, usually a gas. A person suffering from RADS will have shortness of breath and chest tightness severe enough to seek medical attention within 24 hours of the exposure. After recovery from the initial massive exposure, the patient will likely have airways that remain excessively responsive or "twitchy" to stimuli from the agent that caused the initial symptoms or other agents. Almost all patients with RADS will have excessively responsive airways for three months, and 50% to 60% will still have excessively responsive airways 18 months later.